A pseudo-random code (PN code) whose self-correlation characteristic has a sharp peak value is used in many fields, aiming descrimination of a specific signal among a plurality of signals.
One example is the field of radars and sonars in which a received wave, modulated by such a pseudo-random code, then transmitted and reflected back from a reflecting object, is correlated with a reference signal sequence (pseudo-random code) to descriminate a reflected target wave for purposes of distance measurement, etc.
A generally used pseudo-random code is a binary sequence code such as M sequence code or GOLD code sequence.
The self-correlating function of such a pseudorandom code has a nature that its side lobe value does not become zero. FIG. 4 shows such a self-correlating function of an M sequence code.
Therefore, in an environment with a number of reflecting objects, an increase in the cumulative side lobe value causes the peak value of the self-correlating function to be masked, and unables proper detection of the position of a target reflector.
Also in a spread-spectrum multi-channel communication system (hereinbelow abbreviated to SSMA communication system), when combining a plurality of pseudorandom codes modulated by data to form a transmission signal capable of large-scaled data transmission, the side lobe value of the correlation output, which is a received output of a receiver, is increased similarly to the foregoing example, and disturbs data demodulation.